Anti-terrorist police in France yesterday arrested the suspected military leader of the Basque separatist group Eta, Garikoitz Aspiazu, in what was hailed as a major blow against the group.

Aspiazu, whose alias is Txeroki or Cherokee, is believed to be a key member of Eta's leadership and part of a hardline faction that pushed for an end to peace talks with the Spanish government and return to violence two years ago.

As the man in charge of Eta's armed units, he is assumed to have been behind the wave of killings since then.

He is also wanted in connection with the killing of a judge, a plot to kill Spain's King Juan Carlos and with a bomb attack on the Socialist party's former youth leader.

Aspiazu, 35, was arrested in the early hours of yesterday near the French Pyrenean ski resort of Cauterets. An unnamed woman, also reported to be an Eta member, was arrested with him.

The Spanish media reported that two computers found with them were being analysed for clues which might help track down other Eta members. Arms and false documents were also reportedly found.

"This arrest shows once again the strong commitment of the French police and gendarmerie and the excellent cooperation between France and Spain in the fight against Basque terrorism," Nicolas Sarkozy, the French president, said.

The French interior minister, Michèle Alliot-Marie, added: "There will be a certain number of operations [in France] first and then [Aspiazu] will probably be handed over to the Spanish judiciary."

The arrests came five days after the French police detained two suspected members of an Eta armed unit, Ugaitz Astiz Arangoa and Joseba Mikel Olza Puñal, as they cycled through Tarascon-sur-Ariege in south-west France.

It also came as another Eta leader signalled he would fight extradition moves from Northern Ireland to Spain. Iñaki de Juana Chaos, who is wanted for allegedly writing a letter to be read out in his name encouraging Basque terrorism, appeared at a Belfast hearing yesterday.

His lawyers described documents provided by the Spanish authorities as a "fundamentally flawed arrest warrant" and insisted that "the Spanish government have clearly made an error in law."